Grinding mills such as ball mills are commonly used for crushing ore. A typical grinding mill comprises a large rotatable drum containing grinding media (typically steel balls having a diameter of three inches or more). Ore in the form of rocks is dumped into the drum. As the drum rotates, the significant impact forces generated by multiple collisions between the ore, drum and grinding media gradually crushes the ore into small particles which are ultimately removed from the drum for further processing.
The impact forces produced during operation of the grinding mill also result in degradation of the grinding media and the inner lining of the drum. Steel chips or particles break away from the grinding media, eventually wearing the media down to a size at which they lose much of their effectiveness. Worn media and media chips, particles, etc. having a size smaller than the diameter of the drum's discharge outlet are eventually flushed through the mill's discharge trunnion, together with the crushed ore. New grinding media must be added to the drum on a continual basis to replenish the worn media. Furthermore, the worn media, chips, particles, etc. discharged from the drum must somehow be separated from the crushed ore. That can be a time consuming, expensive, labour-intensive process. It is also necessary to regularly replace the inner liner of the drum, since the grinding process also wears out the liner.
A variety of hard drum liner materials have been used in an effort to prolong the life of a grinding mill drum liner. Magnetic liner materials have also been employed, in part because such materials have improved wear-resistant characteristics, and in part because such materials can magnetically attract and retain on the liner itself chips or particles broken away from the grinding media. See for example U.S. Pat. No. 4,340,616 which discloses a method for decreasing the wear on a surface such as a grinding mill liner by incorporating magnetic material into the liner so as to attract particulate material to and incorporate same on the liner, thereby providing a sacrificial wear-resistant liner surface. Also see U.S. Pat. No. 3,913,851 which discloses a wear resistant grinding mill liner which is magnetically retained in place on the grinding mill drum.
The methodology of U.S. Pat. No. 4,340,616 utilizes a flexible magnetic composite material coated with a magnetite concentrate. Although this may be appropriate for improving the wear resistant capability of a pipe for conveying an abrasive slurry, it is inappropriate for use in a grinding mill, since the high impact forces caused by repeated pounding of the ore rock, steel balls, etc. on the liner quickly destroys the relatively fragile magnetized liner. The present invention overcomes these disadvantages.